Topper started licking the middle 2 toes on his rear foot several days ago, by the second day they were swollen and red and no hair, getting pretty raw. Like you, I couldn't find anything visible to my eye, anyway. We tried to distract, I used tea tree oil near the open areas because he hates that smell, and alternated using an antibiotic ointment, a benadryl ointment, and an anti-fungal drop on the red areas. After 3 days, they are much better and he is less interested, I think a combination of all of the above, especially preventing the licking. The worst night I gave a benadryl pill, too. I thought it might be an insect sting, but they can develop "lick sores" pretty fast! Good luck, I hope your boy's foot clears up soon!